1. Field of Application
The present invention relates to a 4-layer type of stator winding for a rotary electric machine, with the stator winding formed of respectively separate U-shaped segments, and with the ends of leg portions of the segments sequentially connected after the segments have been inserted within respective pairs of stator slots.
2. Description of the Prior Art
In the prior art, types of rotary electric machines such as 3-phase alternators for motor vehicles have been proposed, in which the armature winding (assumed in the following to be a stator winding) has a multi-layer configuration, formed of a plurality of pre-formed U-shaped winding segments (sometimes referred to as “hairpin conductors”}. The legs of each segment are inserted into a pair of slots of the stator, such that a U-shaped portion of the segment (referred to in the following as the head portion) protrudes on one side of the stator and extends between the two slots, while two outer ends of the segment (referred to in the following as the leg ends) respectively protrude from these slots on the opposite side of the stator. Each leg end is shaped by being bent in a clockwise or anti-clockwise direction (in general, after insertion into the slots) to enable connection to other segments. The part of a segment leg that is contained within a slot, as a conductor layer, will be referred to as the intra-slot portion.
Each leg end is connected to a leg end of a specific other segment, such that the segments are sequentially connected to form turns of the winding. Each intra-slot portion of a segment is located in a specific one of a plurality of layers, whose positions extend successively radially.
The assignee of the present invention has previously proposed (in Japanese patent publication number 2000-092766, referred to in the following as reference document 1) such a stator winding, having six conductor layers in each stator slot, and utilizing three sizes of segment, i.e., large, medium and small segments. However this has various disadvantages, such as the need to have a number of different types of segments, and complexity of establishing connections between the sets of six segment leg ends protruding from each slot, so that such a stator winding presents substantial manufacturing difficulties.
Based on that prior art, it would be readily possible to envisage a 4-layer sequential segment connection stator winding, having only four conductor layers per slot, and having only two types of segment, i.e., large and small. The features of such a stator winding will be described referring first to FIG. 9. The aforementioned four layers will be referred to in the following as the first layer S1, second layer S2, third layer S3 and fourth layer S4 (the first layer S1 being at the most radially inward position, and the fourth layer S4 being at the most radially outward position). The aforementioned two types of segment are designated as a small segment 50 whose legs are respectively disposed in the second and third layer positions of two stator slots, and a large segment 51, whose legs are disposed in the first and fourth layer positions, respectively, of two slots. Each of the segments is rectangular in cross-section, thereby enabling a high degree of occupancy of each stator slot by the conductors, when the intra-slot portions are stacked in successive radially extending layers.
As shown, each of the leg ends of a segment is shaped by being bent appropriately for connection to a leg end of another segment.
This can be more readily understood from the partial oblique view of a completed stator winding shown in FIG. 12, showing the interconnections between the tip portions of pairs of leg ends of respective segments. In FIG. 12, the layer positions of the segment intra-slot portions that correspond to these tip portions are respectively indicated.
FIG. 10 is a conceptual winding diagram which illustrates the interconnection configuration of a set of segments which form one phase winding of this stator winding, with the numbers 8, 17, etc., being respective numbers of the stator slots containing the intra-slot portions of the segments (e.g., with slots 8 and 17 differing in circumferential position by nine slot pitches). In FIG. 10, and also in FIG. 11 described hereinafter, each set of conductors (intra-slot portions) shown corresponding to one slot are arranged in the drawing with the respective successive positions of these conductors, from the left to right sides, corresponding to their respective layer positions within the slot, that is to say with the leftmost conductor being in the first layer position and the rightmost conductor being in the fourth layer position.
The leg ends of one set of the large segments and one set of the small segments are successively connected in a wave-wound configuration to form a first of two circumferentially extending windings, referred to in the following as partial coils, which have mutually opposite winding directions, while a second set of the large segments and second set of the small segments are successively connected in a lap-wound configuration to form a second partial coil. The starting end of the lap-wound partial coil is designated as 601, while the starting end of the wave-wound partial coil is designated as 602.
The respective intra-slot portions of the small segment and large segment that are connected to the starting ends 601, 602 of the two partial coils constitute the first and second layers S1, S2 of the same slot, i.e., slot number 71, as shown. The respective intra-slot portions of the small segment and large segment that are connected to the terminating ends of the two partial coils constitute the third and fourth layers S3, S4 of slot number 8.
These two partial coils can be connected in parallel to form one of the three phase windings that constitute the stator winding.
In the case of Japanese patent publication number 2002-58189, referred to in the following as reference document 2, a multi-layer sequential segment connection stator winding is described which also utilizes three sizes of segment, as for reference document 1 above. A 4-layer sequential segment connection stator winding could readily be envisaged based on reference document 2, in which a phase winding would be configured as illustrated in the conceptual winding diagram of FIG. 11. In this case, the conductors that are located in the layer positions 1 and 2 of the slots are interconnected to form two small partial coils that extend in mutually opposite directions, while similarly the conductors that are located in the layer positions 3 and 4 of the slots are also interconnected to form two small partial coils that extend in mutually opposite directions, so that there is a total of four small partial coils. Pairs of these small partial coils are connected in series to obtain two partial coils, and these can be connected in parallel to constitute one phase winding.
It should be noted that in the following, the term “4-layer sequential segment connection stator winding” is applicable also to a stator winding having a plurality of sets of four conductor layers in each stator slot, as will be made more apparent from embodiments of the invention described hereinafter (e.g., a configuration having layers that can be designated as S1, S2, S3, S4, S5, S6, S7, S8, successively extending radially from S1 to S8).
Such a 4-layer sequential segment connection stator winding configuration has the advantage of enabling a high occupancy factor for the conductors within each stator slot, so that the efficiency of utilizing the cross-sectional area within each slot can be maximized. In addition, efficient cooling of the leg ends of the segments is achieved. For these reasons, such a configuration enables a compact rotary electric machine to be produced which can be compact in size while having a having a high power rating.
However with a type of 4-layer sequential segment connection stator winding that is described in or could readily be envisaged from the prior art, the arrangement of the leg ends of the segments, and operations to connect respective pairs of leg ends (e.g., by welding) is complex, so that manufacture is difficult. Furthermore due to the fact that there be a substantial difference in potential between conductors that are located at adjacent layer positions within the same slot, it is necessary to pay careful attention to providing sufficient electrical insulation between such adjacent conductors within each slot, if the rotary electric machine is to operate with high levels of voltage being developed in (or applied to) the stator winding.
In addition, since in that case there will also be a substantial potential difference between adjacent leg ends that belong to respectively different partial coils, it is necessary to take measures to prevent corona discharge from occurring between these. For that reason, it may be necessary to provide cylinders of an electrically insulating material (e.g., paper insulation) between sets of segment leg ends that correspond to respectively different adjacent layer positions. This is illustrated in FIGS. 12 and 13, in which three cylinders of paper insulation 41 are disposed between each of adjacent sets of leg ends that respectively correspond to the four layer positions. Hence, the manufacturing difficulty is further increased. In addition, although not shown in the drawings, it may also necessary to provide a similar insulation arrangement on the other side of the stator when high-voltage operations is to be implemented, i.e., three insulation cylinders disposed between sets of segment head portions that respectively correspond to the four layer positions.
These problems arise both in the case of a stator having one slot per pole (i.e., with each pair of adjacent slots of the stator containing conductors that are of respectively different phase) and in the case of a stator winding in which sets of mutually adjacent slots each correspond to the same phase (as described in detail hereinafter), with such a set of adjacent slots being referred to herein as an “identical-phase slot set”.
The above problems apply both for types of prior art 4-layer sequential segment connection stator winding that could be envisaged from the prior art of reference document 1 or from the prior art of reference document 2.
Reference document 1 describes a 6-layer sequential segment connection stator winding stator winding in which the intra-slot portions of the large segments constitute the first and sixth conductor layers of each stator slot, the intra-slot portions of the small segments constitute the third and fourth layers, and the intra-slot portions of the intermediate-size segments constitute the second and fifth layers. Theoretically it would be possible to apply the principles described in reference document 1 to produce a 8-layer sequential segment connection stator winding, or a 10-layer sequential segment connection stator winding. However such configurations having more than 4 layers per slot each have the disadvantages (in addition to those described hereinabove of a 4-layer sequential segment connection stator winding derived based on the prior art) that the axial length of the stator winding is increased, due to an increased degree of protrusion of the sequentially connected leg ends, and that it is necessary to use a greater number of different types of segment. Hence, such types of stator winding configuration are less practicable than a 4-layer sequential segment connection stator winding.